With some simple calculations you can see that you need about 1300 $ to get one S7.

Then you can get for the first two weeks with current difficulty about 155$ (1 btc 430$) and then with the next difficulty at least 10% up you will get for next two weeks 140 $.

One month total profit 295$

Then if you calculate the extra about 8% difficulty up every two weeks (and for now what i say is very minimum) then you will see that you will need about 10-12 months to get your money back and then start from 2017 for profit.

You can imagine how much you will earn with that machine in 2017 with halving (50% up the difficulty extra to what you count) at this summer...

No way!

You must bet that the btc price will go at least 100% up !!!!!